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Using Subnet Zero and the All-Ones Subnet

It should be noted that even though it was discouraged, the entire address space including subnet zero and the all-ones subnet have always been usable. The use of the all-ones subnet was explicitly allowed and the use of subnet zero is explicitly allowed since Cisco IOS Software Release 12.0. Even prior to Cisco IOS Software Release 12.0, subnet zero could be used by entering the ip subnet-zero global configuration command.

On the issue of using subnet zero and the all-ones subnet, RFC 1878 leavingcisco.com states, "This practice (of excluding all-zeros and all-ones subnets) is obsolete. Modern software will be able to utilize all definable networks." Today, the use of subnet zero and the all-ones subnet is generally accepted and most vendors support their use. However, on certain networks, particularly the ones using legacy software, the use of subnet zero and the all-ones subnet can lead to problems.

http://www.ietf.org/rfc/rfc1878.txt

http://www.cisco.com/c/en/us/support/docs/ip/dynamic-address-allocation-resolution/13711-40.html

so both 255.255.255.224 and 255.255.255.240 are valid ans and they will not give both together

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All 255.255.255.224,255.255.255.240,255.255.255.248,255.255.255.252,255.255.255.254 are correct Direct broadcast address for given question X.X.X.31 as it has 31 as broadcast so it can have last octet subnet address as :- 0 (255.255.255.224),16(255.255.255.240),24(255.255.255.248),28(255.255.255.252),30 (255.255.255.254) but only in given option with maximum 1's it is option A.Even your answer  255.255.255.224 is correct as well as option A.I think its ambiguous question.

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